The typical optical microscope used for observing an optical characteristic distribution of a sample cannot realize structural observation with a resolving power of less than a half of its wavelength due to a diffraction limit of visible light used for illuminating the sample, i.e. propagated light. Consequently, in the optical microscope the minimum unit for analyzing sample structure is limited to several hundreds of nanometers. However, because images are obtainable as extended visual observation, analysis simplification and microscope structural simplification were achieved.
On the other hand, in the electron microscope capable of sample surface observation with higher resolving power, because an electron beam with high energy is irradiated on a sample surface to be observed, there has been a trend of damaging a sample or increasing the size of the microscope and its complexity.
Also, as for the scanning tunnel microscope (STM) capable of obtaining images with even higher resolution or the scanning probe microscope (SPM) represented by the atomic force microscope (AFM), atomic and molecular images on a sample surface are obtainable and size reduction has been achieved for the units constituting the microscope. However, the physical quantity to be detected is by an interaction, such as a tunnel current or atomic force, caused between a probe and a sample surface. The obtained resolving power of the surface geometric image is dependent upon a probe tip shape.
Under such situation, attention has now been drawn to the near-field optical microscope which utilizes propagated light and detects an interaction occurring between a probe and a sample surface on a near field basis to thereby break through the propagation light diffraction limit as encountered in the above-mentioned optical microscope and adopts the SPM apparatus structure.
In the near-field optical microscope, a probe having a microscopic aperture smaller than a wavelength of the propagated light used in observation causes scattering in a near field occurring on a light illuminated sample surface. By detecting the scattered light, observation on a smaller microscopic region is made possible exceeding the resolving power of optical microscope observation. Also, by sweeping the wavelength of light illuminated on the sample surface, a sample optical property may be observed in a microscopic region.
For a near-field optical microscope, an optical fiber probe is usually used which has a microscopic aperture formed in the tip of an optical fiber by sharpening and coating the periphery with a metal. The scattered light caused due to an interaction with a near field is passed through a probe interior and introduced to a light detector.
Also, light is introduced through the optical fiber probe toward a sample to generate a near field at an optical fiber probe tip portion. It is also possible to introduce the scattered light caused due to an interaction between the near field and a sample surface microscopic texture to the light detector by using a further added light collecting system.
Further, besides the utilization as a microscope, it is possible to locally generate a high energy density near field on a sample surface by introducing light toward the sample through the optical fiber probe. This makes it possible to change a texture or property of the sample surface and realize a high density memory. In such a case, the recorded information can be recorded/reproduced by including a modulation of a wavelength or intensity of light to be illuminated on the sample in the above-mentioned near-field detecting method.
There is proposed, as a probe used for a near-field optical microscope, a cantilever type optical probe in which an aperture portion is formed penetrating through a silicon substrate by a semiconductor manufacturing technology such as photolithography, an insulation film is formed on one surface of the silicon substrate, and a conical formed optical waveguide layer is formed on the insulation film on an opposite side to the aperture portion, for example, as disclosed for example in U.S. Pat. No. 5,294,790. In this cantilever type optical probe, it is possible to transmit light through the formed microscopic aperture by inserting an optical fiber in the aperture portion and coating with a metal film at areas except for a tip portion of the optical waveguide layer.
Furthermore, the aperture portion of the cantilever type optical probe is provided with a ball lens or a lens forming resin in order to collect the light from the inserted optical fiber on the optical waveguide layer tip.
Meanwhile, there is known a cantilever type optical waveguide probe which uses an optical waveguide instead of an optical fiber inserted in a cantilever type optical probe as by the aforesaid U.S. Pat. No. 5,294,790. For example, the cantilever disclosed in U.S. Pat. No. 5,354,985 is structured with a capacitor layer formed to utilize the AFM technology together with an optical waveguide for introducing light to an aperture so that the cantilever can be detected in vibration and flexure amount.
Furthermore, according to the cantilever type optical waveguide probe, laser is illuminated to a cantilever surface. The above mentioned capacitor layer or a piezoelectric resistance layer is omitted such that the AFM technology of detecting a cantilever flexure amount is utilized by the reflection position. Further, a concave formed lens or Fresnel zone plate is formed in an aperture direction on the optical waveguide, and light introduced from the optical waveguide can be collected toward the aperture.
Furthermore, there is also a proposal to use a flat surface probe without having a sharpened tip like the above-mentioned probe. The flat surface probe has an inverted pyramid structured aperture formed in a silicon substrate by anisotropic etching. Particularly, its apex is penetrated by having a diameter of several tens of nanometers. In such a flat plane probe, it is easy to form a plurality on the same substrate, i.e., in an array, by the use of a semiconductor manufacturing technology. In particular, it is possible to use as an optical head suited for optical memory reproduction recording utilizing a near field. By attaching the above-mentioned ball lens in an aperture portion of this flat plane probe, it is possible to collect the light introduced to a flat plane probe surface onto an aperture its portion.
However, the optical fiber probe explained above has a sharpened tip, and accordingly is not sufficient in mechanical strength and not suited for mass production and arraying. Also, because the scattered light is to be detected through an optical fiber, there is a necessity of devising a way to obtain a sufficient amount of light at a detecting portion. Also, where creating a sufficiently large near field through an optical fiber, there is a necessity of devising a way to collect light to the aperture.
Also, in the cantilever type optical probe explained above, because an optical fiber is inserted to the aperture portion to achieve reception of the scattered light from the optical waveguide layer or introduction of the propagated light to the optical waveguide layer, a sufficient amount of light could not be propagated without loss between the optical waveguide layer and the optical fiber.
Furthermore, where a ball lens is provided in the aperture portion, the ball lens cannot necessarily adjust a focal point to a light inlet/outlet surface of the optical fiber or an optical waveguide layer tip portion, thus making it impossible to effect optimal light collection.
Also, in the cantilever type optical waveguide probe explained above, there is a similar problem between the propagation light to the optical waveguide and the optical detector or the propagation light from a light source, to the case of using a cantilever type optical probe as stated above.
The cantilever type optical probe and the cantilever type optical waveguide probe are both difficult to realize particularly arraying in two dimensional arrangement. Also, there are not considered on optical memory information recording/reproduction because of an inherent purpose of utilization as a microscope. High speed scan is difficult over a recording medium.
The flat plane probe explained above is suited for mass production and arraying. Because there is no projected sharpened portion, mechanical strength is sufficient. However, because light collection is achieved by providing a ball lens in the aperture portion, there is a similar problem to the use of a ball lens in the cantilever type optical probe.
Therefore, it is an object of the present invention to provide a probe capable of detecting and creating a sufficient intensity of a near field, in a probe having a conventional microscopic aperture as described above, particularly a near-field optical probe as an optical memory head suited for mass production and arraying in order to realize optical memory information recording/reproduction utilizing a near field.